The Peruvian diplomat, who’s striving to end Cyprus’ 28 years of division by 28 February, has pioneered a ‘single negotiating text’ method to international mediation. Here’s how it works:

If two sides in a conflict refuse to speak to each other, an outsider should listen carefully to what each has to say. When the real sources of tension become apparent, try to draw up a reasonable compromise. This might not be the middle point between the two sides but should appear fair and workable. Then, give the sides time to reflect on the document and ask them for their comments. Once they’ve been received, keep on tweaking the plan until, hey presto!, you have a deal.

“It may take 20 revisions, it may take 50, and it seems like a very slow way to proceed,” de Soto said in a 2001 interview. “But it is remarkable as you go along in a negotiation how the parties’ more extreme negotiating positions can gradually fall by the wayside, a bit like peeling an onion.”

The formula helped de Soto to end one of the 1980s’ most heinous conflicts – El Salvador’s civil war.

From its start in 1980, to the de Soto-brokered truce 12 years later, the fighting between US-funded government troops and left-wing guerrillas, the Farabundo Martí National Liberation Front (FMLN) claimed 70,000 lives. It became synonymous with death squads, the murder of Archbishop Oscar Romero while he celebrated mass and crimes such as the 1981 El Mazote massacre when American-trained soldiers butchered some 800 civilians in a north-eastern hamlet. And it became a cause célèbre for critics of US foreign policy; the Reagan administration sent billions of dollars in aid to the right-wing government in San Salvador because it perceived it as a bulwark against communism.

De Soto’s involvement in El Salvador began when Latin American leaders pleaded with Javier Perez de Cuellar, the then UN secretary-general, to intervene in 1986. Early the following year de Cuellar gave his assistant de Soto the arduous task of stopping the violence.

Until 1989, de Soto’s work was largely one of research about the conflict and its causes. He was aided by his colleague Francesc Vendrell, who built up contacts with what de Soto called the “FMLN’s roving political-diplomatic commission”, who often took part in fringe meetings at conferences by the non-aligned movement – countries not allied to the superpowers. (Vendrell was later appointed head of a UN mission to Afghanistan in 2000).

The UN-sponsored peace talks only took off in April 1990. That followed Washington’s decision to drop its opposition to outside mediation – a move presaged by outrage at how Salvadorean military officers ordered the killing of seven Jesuit priests, their housekeeper and her daughter in November 1989.

The first major achievement of the talks was an April 1991 reform, changing the role of the army from an open-to-interpretation “defender of democracy” to a territorial force, forbidden from making politically motivated decisions. Some months later, it was eventually agreed that FMLN activists could join the new security forces. But the definitive settlement, copper-fastening the cessation of hostilities, was not signed until 16 January 1992.

During those six years de Soto succeeded in disproving that rhyme about patience never existing in a man. Yet not everyone was happy with him. William Walker, then the US ambassador to El Salvador, told reporters in 1991 that de Soto was biased towards the FMLN and lacked professionalism. But a 1998 article for Columbia Journalism Review suggested Walker’s view was not shared by other diplomats in the country.

Despite the suspicions he aroused, de Soto has become something of a role model for subsequent American peacemakers. His ‘single negotiating text’ approach has been aped by Jimmy Carter; the ex-president used it during the Camp David talks on the Middle East. It has been employed too by George Mitchell, the US emissary who secured the Good Friday peace agreement in Northern Ireland.

George Vassiliou, the former Greek Cypriot president who has led negotiations on his government’s EU accession, believes de Soto is showing the same kind of tenacity in Cyprus as he did in El Salvador.

De Soto has been the UN envoy to the Mediterranean island since 1999 but for much of that time was unable to bring the Greek and Turkish Cypriot leaders Glafcos Clerides and Rauf Denktash to the negotiating table. That changed in January 2001, when he began chairing twice-weekly talks between the two ageing politicians at a building on the passenger terminal of Nicosia’s one-time international airport.

After months of painstaking deliberations, de Soto helped draft a blueprint for a possible solution. Presented to both sides by UN Secretary-General Kofi Annan, it was based on the idea of having two states on the island, linked with a central administration, involving both communities. Neither side was entirely happy with the plan – the Greek Cypriots believe it does not adequately address the situation of their people whose property was confiscated in 1974; the Turkish Cypriots complain it did not give them the same veto rights they had during a power-sharing exercise in 1960.

The difficulties in securing a breakthrough have also been compounded by Denktash’s recent ill-health and his general intransigence (something which has led Turkish Cypriots more favourably disposed to compromise to call for his resignation).

In the end, all hopes that a unification deal could be reached before last month’s EU summit in Copenhagen evaporated; but a new deadline of 28 February for securing an agreement has been set by the UN.

Vassiliou feels de Soto is frustrated with Denktash but that he is such a skilled diplomat “he would never tell you that”. “He’ll never take no for an answer,” Vassiliou told European Voice. “He never despairs but keeps on trying.

“He’s an extremely able and straight person. He’s very honest and he has a very objective approach in his work. I believe he has gained the confidence of both sides. Although there have been a lot of people critical of the Annan plan, I haven’t seen anybody address their criticism to de Soto. That’s another proof of his fairness.”

Hilmi Akil, Denktash’s EU representative, doesn’t exactly concur. He argues most of today’s problems emanate from a 1964 UN Security Council resolution, which recognised the Greek Cypriot administration in Nicosia as the only legitimate government on the island.

“De Soto is the last in a long list of special representatives of the UN secretary-general,” said Akil. “Subconsciously, he might be feeling he has to give more to the Greek Cypriots because they are seen as the legal government. And the document came out more in favour of the Greek Cypriots, although I’m sure Mr de Soto will say it is fair and balanced.”

However Michael Emerson, from the Brussels-based Centre of European Policy Studies think-tank, says such criticisms are not justified. “The Annan plan was a very fine piece of staff work, which he [de Soto] oversaw. It’s fairly judged. Both sides are unhappy with it, maybe equally so.”

A former UN chief of mission in Cyprus, James Holger, has labelled de Soto a “cool cat” with a “wonderful sense of humour”.

“Alvaro de Soto is the UN troubleshooter to handle delicate problems,” Holger said in early 2000.

Formerly a civil servant in Lima and a diplomat in New York, de Soto was hired as an advisor to de Cuellar in 1982.

He had something of a baptism of fire – just weeks after he joined the UN’s top office, he had to flank de Cuellar during his – unsuccessful – efforts to prevent Britain from declaring war against Argentina over its invasion of the Falkland Islands.

The boundless patience which he has developed seems to extend to his leisure pursuits. Vassiliou recalls how the theatre buff has been known to visit London to soak up several consecutive plays.

Among the writers he admires are the Czechoslovakian-born Englishman Tom Stoppard. And it’s tempting to speculate whether this excerpt from the 1974 Stoppard play Travesties could have influenced his style of chairmanship (especially if the word ‘stories’ is replaced with ‘problems’): “Without spectators, the world would be imperfect: the participant, absorbed as he is in particular things and pressed by urgent business, cannot see how all the particular deeds in the realm of human affairs fit together and produce a harmony, which itself is not given to sense perception; and this invisible in the visible would remain forever unknown if there were no spectator to look out for it, admire it, straighten out the stories and put them into words.”

Perhaps, though, that might only sum up part of de Soto’s extraordinary career. Unfailingly polite, he’s not averse to speaking his mind (although he prefers to do so in private rather than in public) – as indicated by some of his suggested guidelines on how to conduct negotiations: “Never try to trick anyone. You will usually be found out and whatever you achieve, the trick will not be durable.

“Second, do not try to sweeten the state of play just to ingratiate yourself with one of the parties. Another way of saying that is, don’t tell a party to a dispute or a conflict what he wants to hear but rather what the situation really is.

“Third, don’t negotiate side deals. The end result should be transparent, as distinct from the negotiations themselves, which should be confidential. Just as there exists the fog of war, in which the first victim is the truth, there should exist the fog of diplomacy or the fog of good offices in which the truth should only come out as the end result.”